The present invention is used to expand tubing used in chillers. Chillers are a component of a refrigeration system typically being of a shell-and-tube design, the shell typically comprised of steel and the tubes being comprised, of copper or copper alloy. Chillers are used for large industrial process cooling and commercial air conditioning. The chiller comprises a plurality of tubes, from a few tubes to a few thousand tubes, depending upon the capacity of the refrigeration system, extending through the shell structure. The shell structure has a longitudinal axis and a head at either end of the shell structure. The heads typically act as manifolds for a fluid. The tubes extend through the shell structure generally parallel to the longitudinal axis of the shell structure. Within the shell structure, the tubes extend between tube sheets in the heads. The tube sheets include a plurality of apertures into which the tubes are inserted. The tubes are plastically deformed by expansion into the tube sheet structure to form an extremely tight joint to prevent a first fluid flowing through the tubes from leaking around the joint and behind the tube sheet and mixing with a second fluid flowing over the tube bundle. The tight joint also prevents the second fluid from leaking across the joint and mixing with the first fluid flowing in the tubes. Although very uncommon in chiller applications, if a 100% leak-proof seal is demanded, a weld can be placed at the joint between the tube and the tube sheet.
The shell structure of the chiller can be of varying lengths, and therefore contains tube supports for the plurality of tubes at one or more locations along the length between the tube sheets. The tube supports include a plurality of tube apertures into which the tubes are inserted to form a tube bundle. Tube supports are axially located along the tubes, providing them with support and the problem of leakage across the joint is not an issue unless the tube is cracked. Refrigerant fluid and water are the fluids typically used in these heat exchangers. One of these fluids flows through the tubes and exchanges heat with the other fluid flowing over the tubes. In some designs, water flows through the tubes and refrigerant flows over the tube bundle to accomplish heat exchange. In other designs, the refrigerant flows through the tubes and water flows over the tube bundle to accomplish heat exchange. For the purposes of this invention, the particular design is not important. However, it is important that in either design, the flow paths of the fluids remain independent so that mixing of the fluids is minimized or prevented. Depending upon the location of the chiller within the refrigeration cycle, the chiller may act as a condenser or as an evaporator. Again, the particular application is not important for this invention. It is important, however, that mixing of the two different fluids be minimized or prevented, while also providing support to the tubes in the chiller.
These tube supports provide mechanical support to the plurality of tubes and maintain their separation so they can be effective in providing heat transfer. During operation, to reduce any noise due to vibration of the tubes against the apertures in the tube support, it is necessary to secure the tube against the corresponding aperture in the tube support. This gap can also lead to damage to the tube during the life of the chiller. The damage can be the result of repeated vibration and fatigue. Alternatively, foreign materials, sometimes referred to as crud, can be trapped in the gap and can chemically attack the tube. Thus, it is desirable to close the gap in order to eliminate or reduce the vibration and prevent crud entrapment. The tube can be secured in the tube support by a variety of different methods that accomplish this purpose. Currently, this expansion is most economically performed by a tube rolling technique which mechanically expands the tube outer diameter against the circumference of the tube aperture in the tube support by permanent plastic deformation of the tube using a mandrel and a series of circumferential rollers. The rollers are forced against the tube by the mandrel which expands the tube. This mechanical action can thin the tube as the action of the rollers against the tube inner diameter can also remove material as the tube is expanded. This tube expansion ideally expands the tube outer diameter into contact with the circumference of the tube aperture in the tube support uniformly 360° about this circumference. Such ideal expansion is sometimes referred to as touch expansion. Not all expansions are ideal. On occasion, the tube can become highly distorted or upset along one or more arc segments of the aperture in the support plate so as to extremely hinder or prevent its removal, particularly if the location of the rollers with respect to the tube support is not carefully controlled. This undesirable expansion is sometimes referred to as an overexpansion, and is to be avoided when possible. The problems associated with tube rolling introduce into the tubes manufacturing variables that can lead to increased failure rates. Reliability can be improved if these variables are eliminated. In addition, tube rolling is accomplished by rolling each tube individually into each tube support.
Tube expansion of tubes in structures such as tube supports, tube sheets and baffles has been accomplished by an ideal expansion of the tube outer diameter against the inner diameter of such structures. The nuclear industry has accomplished this expansion in a controlled manner. For example, U.S. Pat. No. 4,889,679 outlines apparatus for locating a tube in relation to a tube sheet, baffle or support plate in a nuclear reactor steam generator and then expanding the tube sheet against the support plate once it has been properly located. As can be appreciated, the proper location of the tube in relation to a related structure in a nuclear reactor is exceedingly important, as failure to properly expand the tube or expanding an improperly located tube can lead to premature tube failure, having disastrous consequences, including contamination of non-radioactive secondary water with radioactive primary water, which can lead to radioactive contamination of the entire secondary system, which is supposed to remain non-radioactive. To achieve the necessary degree of quality assurance and reliability demanded by the nuclear industry, this patent sets forth a combination of an eddy current probe and an expandable bladder-type probe. The probe is inserted into each tube in the steam generator and the location of the tube with respect to an individual tube support plate, baffle plate or tube sheet is determined to within three thousandths of an inch (0.003″). The expandable bladder is then activated and the tube is expanded. The probe is then moved to locate the next support plate, baffle plate or tube sheet. The eddy current probe can inspect the extent of the expansion of the tube into the apertures in the structure. As one may expect, this operation is expensive and time consuming, considering that a steam generator includes hundreds and even thousands of tubes with multiple supports, baffle plates and tube sheets. However, due to the criticality of the operations and the overriding concern with safety, this time consuming, costly operation is acceptable, while cost-savings improvements that do not provide at least the same reliability and safety are not acceptable, and indeed will not even be considered.
A related patent is U.S. Pat. No. 4,649,493 which describes a similar apparatus for locating, inspecting and expanding a tube at a tube location adjacent to a support plate, baffle plate or tube sheet in a nuclear reactor steam generator. Again, because of the reliability and safety concerns in a nuclear reactor, each tube is expanded sequentially at each location as a precise determination is made of the location of the tube with respect to the related structure.
Another patent, U.S. Pat. No. 5,791,046 to Schafer issued Aug. 11, 1998, incorporated herein by reference, sets forth apparatus for expanding a sleeve in multiple locations against a defective region of a tube to accomplish a tube repair in an application such as a nuclear reactor heat exchanger. The apparatus disclosed in the patent utilizes the eddy current detector to locate the location and size of the defect and a plurality of bladders to expand a single sleeve in a plurality of locations to secure the sleeve against the tube and to reduce the leak rate between the tube and the sleeve. The location of the sleeve with respect to the tube defect is the critical aspect of the Schafer invention, as the defect can be located at any position along the tube.
What is needed is apparatus that permits the simultaneous expansion of a tube at multiple locations along its length corresponding to the position of the aperture in the tube support. This expansion should both simultaneously expand the tube against the tube support apertures, while assuring reasonable accuracy of the location of the tube with respect to the tube support, but without requiring overly accurate determinations of the location of the tube with respect to the tube support. The apparatus should also produce ideal expansions to uniformly expand the outer diameter into contact with the circumference of the tube aperture.